Achieving both security and efficiency is the challenging issue for a data outsourcing service in the cloud computing.

Proof of Storage with Deduplication (POSD) is the first solution that addresses the issue for the cloud storage. However, the validity of the POSD scheme stands on the strong assumption that all clients are honest in terms of generating their keys. We present insecurity of the scheme

under new attack model that malicious clients exploit dishonestly manipulated keys. We also propose an improvement of the POSD scheme to mitigate our attack.

We consider the client-server setting for the concurrent composition of secure protocols: in this setting, a single server interacts with multiple clients concurrently, executing with each client a specified protocol where only the client should receive any nontrivial output. Such a setting is easily motivated from an application standpoint. There are important special cases for which positive results are known - such as concurrent zero knowledge protocols - and it has been an open question explicitly asked, for instance, by Lindell [J. Cryptology\'08] - whether other natural functionalities such as Oblivious Transfer (OT) are possible in this setting.

In this work:

1. We resolve this open question by showing that unfortunately, even in this very limited concurrency setting, broad new impossibility results hold, ruling out not only OT, but in fact all nontrivial asymmetric functionalities. Our new negative results hold even if the inputs of all honest parties are fixed in advance, and the adversary receives no auxiliary information.

2. Along the way, we establish a new unconditional completeness result for asymmetric functionalities, where we characterize functionalities that are non-interactively complete secure against active adversaries. When we say that a functionality F is non-interactively complete, we mean that every other asymmetric functionality can be realized by parallel invocations of several copies of F, with no other communication in any direction. Our result subsumes a completeness result of Kilian [STOC\'00] that uses protocols which require additional interaction in both directions.

In the setting of cryptographic protocols, the corruption of a party has traditionally been viewed as a simple, uniform and atomic operation, where the adversary decides to get control over a party and this party immediately gets corrupted. In this paper, motivated by the fact that different players may require different resources to get corrupted, we put forth the notion of {\\em resource-based corruptions}, where the adversary must invest some resources in order to do so.

If the adversary has full information about the system configuration then resource-based corruptions would provide no fundamental difference from the standard corruption model. However, in a resource ``anonymous\'\' setting, in the sense that such configuration is hidden from the adversary, much is to be gained in terms of efficiency and security.

We showcase the power of such {\\em hidden diversity} in the context of secure multiparty computation (MPC) with resource-based corruptions and prove that it can effectively be used to circumvent known impossibility results. Specifically, if $OPT$ is the corruption budget that violates the completeness of MPC (the case when half or more of the players are corrupted), we show that if hidden diversity is available, the completeness of MPC can be made to hold against an adversary with as much as a $B\\cdot OPT$ budget, for any constant $B>1$. This result requires a suitable choice of parameters (in terms of number of players and their hardness to corrupt), which we provide and further prove other tight variants of the result when the said choice is not available. Regarding efficiency gains, we show that hidden diversity can be used to force the corruption threshold to drop from 1/2 to 1/3, in turn allowing the use of much more efficient (information-theoretic) MPC protocols.

We achieve the above through a series of technical contributions:

o The modeling of the corruption process in the setting of cryptographic protocols through {\\em corruption oracles} as well as the introduction of a notion of reduction to relate such oracles;

o the abstraction of the corruption game as a combinatorial problem and its analysis; and, importantly,

o the formulation of the notion of {\\em inversion effort preserving} (IEP) functions which is a type of direct-sum property, and the property of {\\em hardness indistinguishability}. While hardness indistinguishability enables the dissociation of parties\' identities and the resources needed to corrupt them, IEP enables the discretization of adversarial work into corruption tokens,

• 8+ years of experience in tamper resistant hardware design and at least 5 years of experience in developing DPA resistant hardware and products that use algorithms such as DES, 3DES, AES, RSA and ECC.

• Deep knowledge of the statistics of DPA, sources of information leakage in hardware and engineering tradeoffs between different countermeasure choices

• 3+ years experience in performing DPA on a range of real-world systems, form factors and algorithms, including experience with developing DPA test fixtures for embedded devices, setting up scopes and measurement apparatus, and applying signal processing and DPA techniques on the collected traces

In this paper, we propose an elaborate geometric approach to explain the group law on Jacobi quartic curves which are seen as the intersection of two quadratic surfaces in space. Using the geometry

interpretation we construct the Miller function. Then we present explicit formulae for the addition and doubling steps in Miller\'s algorithm to compute Tate pairing on Jacobi quartic curves. Both the addition step and doubling step of our formulae for Tate pairing computation on Jacobi curves are faster than previously proposed ones.

Finally, we present efficient formulas for Jacobi quartic curves with twists of degree 4 or 6. For twists of degree 4, both the addition steps and doubling steps in our formulas are faster than the fastest result on Weierstrass curves. For twists of degree 6, the addition steps of our formulae are faster than the fastest result on Weierstrass curves.

In this paper we attack round-reduced Keccak hash function with a technique called rotational cryptanalysis. We focus on Keccak variants proposed as SHA-3 candidates in the NIST\'s contest for a new standard of cryptographic hash function. Our main result is a preimage attack on 4-round Keccak and a 5-round distinguisher on Keccak-f[1600] permutation --- the main building block of Keccak hash function.

for the robustness of S-boxes to \\emph{Differential Power Analysis} (DPA):lower \\emph{transparency order} implying more resistance. However most cryptographically strong Boolean functions have been found to have high \\emph{transparency order}. Also it is a difficult problem to search for Boolean functions which are strong cryptographically, and yet have low \\emph{transparency order}, the total search space for $(n,n)$-bit Boolean functions being as large as $n2^{2^n}$. In this paper we characterize \\emph{transparency order} for various classes of Boolean functions by computing the upper and lower bounds of \\emph{transparency order} for both

even and odd numbers of variables. The transparency order is defined in terms of \\emph{diffusion} properties of the structures of Boolean functions namely the number of bit flips in the output of the functions corresponding to the number of bit flips at the input of the function. The calculated bounds depend on the number of vectors flipping the input of S-box for which bias of probability of S-box output bit deviates from the value of 0.5. The \\emph{transparency order} is found to be high in the class of those Boolean functions which have larger cardinality of input differences for which the probability of output bit flip is 0.5. Also we find that instead of \\emph{propagation characteristics}, \\emph{autocorrelation

spectra} of the S-box function $F$ is a more qualifying candidate in deciding the characteristics of \\emph{transparency order}. The relations developed to characterize \\emph{transparency order} aid in our constrained random generation and search of a class of

We propose two basic NIZK arguments, one for Hadamard product of two vectors, and another one for a shift of a vector. The first argument is based on the corresponding argument of Lipmaa (TCC 2012), but makes use of Fast Fourier Transform and Pippenger\'s multi-exponentiation algorithm to achieve quasilinear (as opposed quadratic) computational complexity. The shift argument seems to be novel.

Based on the new basic arguments, we propose a NIZK argument for subset sum. This seems to be the only known (direct) sublinear NIZK argument for some other NP-complete language than Circuit-SAT\\@. Moreover, it is significantly more efficient than the known sublinear Circuit-SAT arguments by Groth (Asiacrypt 2010) and Lipmaa. In addition, we show that the new arguments can be used to speed up the recent range argument by Chaabouni, Lipmaa and Zhang (FC 2012). Finally, we combine the subset sum argument and the range argument to propose a direct sublinear NIZK argument for another NP-complete language, decision knapsack.

Batch signature verification detects whether a batch of signatures contains any forgeries. Batch forgery identification pinpoints the location of each forgery. Existing forgery-identification schemes vary in their strategies for selecting subbatches to verify (individual checks, binary search, combinatorial designs, etc.) and in their strategies for verifying subbatches. This paper exploits synergies between these two levels of strategies, reducing the cost of batch forgery identification for elliptic-curve signatures.